Okay, here is how it works. It is kind of like a scratch fusion, but you make images to add it into the official game. You also need to explain the type of boss it is, like if it is the first boss, a secret boss, or anything like that. You also need to add music to the boss. Add your bosses to the studio. And DO NOT fully create the boss, only make the idea. this is old lol please dont try to submit something
Credits to A Sincere Man for the original idea, and @orangeyoshi8000 for the second idea.